1. Field of the Invention
The invention relates to color image processing, more particularly to a method and apparatus for contrast enhancement of color images.
2. Description of the Related Art
A variety of image compression techniques are available in the art to reduce the required bandwidth during signal transmission and the required memory space for storing digital images. During compression or decompression, high frequency signals are sacrificed to attain compression efficiency and real-time decompression. However, the image that is obtained after decompression is often blurred and dull. Thus, there is a need to perform contrast enhancement to restore the clarity and brightness of the image.
For black-and-white images, the dynamic range of intensity or luminance can be increased to attain contrast enhancement. However, for color images, in addition to luminance, color saturation and hue should also be taken into account.
It is known that the same color information in one color space has corresponding component values in another color space. Thus, contrast enhancement can be achieved in different color spaces. For example, when contrast enhancement is done in the YCbCr color space, it has been found that, although the luminance of the image is increased, a less saturated image is obtained when the contrast enhancement factor is increased.